Guerilla guide to CNC machining

[Ian] wrote in to tell us about the Guerilla Guide to CNC Machining and Resin Casting. He came across it in the reference links to another project and says he wish he knew about it a long time ago. We took a look and there’s a mountain of useful information in the guide, which is written by [Michal Zalewski]. We won’t pretend that we’ve read the whole thing, there’s days worth of information here. But we will. The range of topics includes types of milling machines, milling materials, software options and use, safety, and the list goes on. Bookmark this (don’t forget the second volume), it might be just the thing to get you through the holiday with your family.

17 thoughts on “Guerilla guide to CNC machining”

That’s rather funny as I have been taking thorough notes on his guides and fantastic work since the dial-a-threat was posted.

It is far from definitive but has a solid case for casting parts instead of machining them every time.

Now we just have to find an equally impressive work on building a CNC machine. CNCzone is all fine and dandy but all forums have their cultures, norms, and quirks. Anyone have an idea where to find thorough information on say, the technical pros and cons between 80/20 vs MDF framing including technical data; not just some buffoon’s opinion. Ex. 80/20 seems fine and good sans the price however it has way less mass than MDF thus greater vibration induction will occur. Given that where is the sweet spot? What are the ideal options for framing? Does the author acknowledge multiple ideals based on different specification criteria?

First: CNC machining is phenomenally cool. I’m absolutely amazed by the affordability of desktop milling today. If you feel the same way and think you have the skills to use one, then get started! I bought mine (a Taig CNC ready mill) a few years ago and love it.

Regarding the article: Unfortunately, the only aspect that impresses me is its length. It may be worth a read, but is so full of misinformation you shouldn’t trust anything in it. There is one point I agree with, though: Building your own CNC milling machine is likely to be a huge time sink that results in a mediocre machine (and in the end will probably cost more than commercial alternatives). Unless you really, truly know what you are doing, start with an off the shelf mill, preferably CNC or CNC-ready unless you already have access to a machine shop.

Ketchup: The only sensible material for the structure of a real milling machine (tabletop or otherwise) is steel. You can make a decent CNC tool for cutting soft materials out of other stuff, just don’t ask me to call it a milling machine. CNCzone is a good site for information on a wide variety of CNC topics, including DIY.

I have been playing around with a Fireball CNC which is a low end machine made mostly from MDF (but has some impressive capabilities). I have no complaints with it. The Fireball came as a kit that I bolted together.

I have seen mixed reviews on using MDF. In my limited opinion, the success of using MDF is mostly with who builds it, their skill level and if the basic design of the machine is solid. The only real complaint that I have seen is some of the tolerances can very depending on humidity. Even that most likely can be overcome by properly sealing it.

I have been able to figure out only some of what is covered in this guide after two years. Finding all this information in one spot is incredible. Time to go play!

I have been wanting to use a makerbot or a reprap to make parts for robots and other things. But after seeing this. I think I may go the CNC route, the issue I have had with 3d printers is the quality and after seeing some of the things he made I am sure its CNC for the win. I hope to comb through the site and see what he has to say about resins and other material to make your molds from.

Don’t forget cast iron – most milling machine ways are cast iron and the table steel. Also the column/body of many (nearly all of the good ones) lathes/mills etc are cast iron because it has good vibration damping characteristics.

The problem for DIY is casting a cast iron body, and making the ways if you don’t have access to a surface grinder – people turn to much less ideal things… like drawer sliders or 608 bearings on steel angle.

Evan: I have listed some examples that I consider to be misinformed below.

swighton: My bad – Cast iron is indeed an excellent material for mill structures. Another advantage it has over steel is less internal stress, and therefore better stability (less warping) when machined.

My full CNC 4th axis retails for around $375 (assuming a 4th channel is available in the controller), nowhere close to the $1000 amount cited.

Backlash is not even mentioned in the section on accuracy.

The typical table speeds claimed range from barely detectable to intolerably slow. My mill, which is nothing special, has rapids six times faster then the fastest speed mentioned.

TiAlN coatings have no value for tabletop milling. These coatings come into their own when operations heat up on industrial equipment, table top energy is so low that my end mill is generally cool to the touch, even when cutting steel (using only compressed air cooling). It would have been better to mention that HSS tools are sharper than carbide and often work better for our purposes.

The recommended spindle speeds (6-20 kRPM) rule out many useful operations. I’m much happier with my 1-10 kRPM spindle, though I wish I had an even slower speed available. I think high speed spindles are for specialized uses.

The use of inexpensive tool holders, which clamp the tool with a set screw and are available for some spindles, is ignored in the discussion of tool holding.

High helix angles are claimed to be “important for aluminum”, which is true if we are talking about a VMC or even Bridgeport, but has little relevance at the slow rates of material removal on desktop mills.

I don’t mean to condemn the article. Just read it with a good dose of skepticism and check the facts before acting on them.

@Ken,
From the looks of it, it is rather old. It speaks of deposition printing as some pipe dream of the future. It also makes no mention of the many DIY cnc machines now available open source or damn cheap.

I’d say that yes it very much is a guerrilla guide and it could probably use an update just like all guides of the sort.

@Ken – I’m the author of that doc. I appreciate your feedback, and there is a good chance it’s inaccurate in quite a few places – but I think that on quite a few counts, you simply overlooked some stuff:

3) Form cutters: these cutters are generally not available or practical for the cutter diameters and processes discussed in the guide. There is a mention of more exotic endmill geometries later on, though.

4) Table speeds: are you sure you’re not mixing up mm/sec and in/min?

5) RPM: the doc is pretty much exclusively about “specialty” applications: machining prototyping boards with sub-1mm cutters. For this application, high RPM is quite desirable.

6) TiAlN: may not matter in many cases, but fundamentally, is beneficial when working in plastics at high RPM, because it reduces tool temperature slightly.

@anon: the doc does mention MakerBot, Reprap, etc, and has a discussion of their limitations.

The section where he rules out undercuts is prefixed with “ignoring more complex cutter geometries at the moment.” If it isn’t a square/ball end mill, a drill, at that stage of the tutorial, it’s reasonable to rule out. Really, arbitrary undercuts aren’t possible… just a certain class of them.

High spindle speeds are useful for what he does, which is mold making. For soft materials like aluminum, really a 20k spindle would be great. High feeds, nice surface finishes, awesome. His mill isn’t even rigid enough to touch steel.

Seriously the guy has been doing plastics pretty much exclusively. It’s a huge chunk of writing and I don’t see how it’s FULL of misinformation.

Also proper plastic deposition kinda still do all that well. Rep rap parts still don’t even come close to the quality of parts off a CNC. Hell, we don’t even have support material.

Why advise against building your own CNC router? Anybody with a little patience can build a machine that can handle foam, wood, and aluminum and still keep great tolerances.

Don’t confuse a router with a milling machine. I’ve seen exactly 1 diy milling machine, and yes it was steel. I personally prefer steel tube over aluminum extrusion (for the added weight, cost, etc) but the extrusions are more than sufficient for most routers (mind you I’m not talking about the toothpick 1010 size).

Sorry if I sound critical about CNC milling info and machines, but if so it is because CNC milling is really hard to to – at least once we bring metals into the picture (and the article definitely speaks of metals). Even aluminum require a seriously amount of rigidity to cut at any significant rate of removal.

My advice about buying off the shelf was based on the assumption that we are talking about cutting metal. Building a machine to cut wax or foam is a much easier proposition.

MZ: Sorry for a few off-base criticisms. I scanned the article for specifics very quickly and missed on a couple of my points. In particular, I completely botched the conversion from mm/s to in/min.

However I stand by my warning to reader. My biggest complaint is that the doc fails to set its boudaries: It mentions operations on all sorts of materials, including steel, and then gives recommendations appropriate for working only the softest stuff. Desktop mills can be used for a wide range of materials, and I find pushing the limits can be very rewarding (though also, at times, frustrating).

I don’t what we are doing differently, but when I cut plastics, my end mill is usually cold to the touch at the end of the operation. Plastics are poor conductors of heat, so the heat generated by cutting is almost completely removed as the chips are ejected during cutting. TiAlN coated end mills are not useful here: they come into their own at ridiculously high temperatures (up to 800C – well above aluminum’s melting point). My supplier of choice for specialty miniature end mills, Harvey Tool, does not even offer TiAlN coating on their plastic cutting end mills, though they do offer amorphous diamond coatings which extend tool life in abrasive materials on some of their general purpose end mills.

By the way, if I had problems with heat build up, I would definitely look at end mills optimized for the material being cut. Plastics are best approached with high rake and clearance angles. You might even consider router bits meant for wood.

Form cutters are readily accessible. Every hardware store and building center I shop at carries Dremel bit #199, which I use to cut O-ring slots. The Harvey Tool miniature dovetail cutters I use are sold by my regular end mill supplier. Ball burs, and others fun cutters are found in various places. More importantly, you can shape your own cutters using blanks on fly cutters, boring heads, and gear cutting arbors.

Not to dogpile, because I agree with you on the Titanium Nitride, but the attitude about DIY CNC IMHO comes across as a bit snobbish.

I use a DIY CNC Mill regularly. Bolting together steel to form a frame for linear rails/ballscrews is not rocket science, and when the average REAL CNC mill costs ~$10K(for a basic HAAS) then it’s stupid to condemn options in the <$2K range.

I would say that the only legitimate reason to CNC a harbour freight is if you don't have room for something larger. After working in industry on Bridgeports I've never been able to be happy with the metal removal rates of anything smaller than a Bridgeport.

If you're going to invest $1000 + on tooling and a CNC conversion, you might as well spend that much on a machine which will continue to pay you back on the investment in time savings.(spindle taper, motors, and ballscrews: none of that transfers)

A bridgeport can bury a 3/8 endmill 5/8 deep in alluminum and handle a couple IPM. You'd be lucky to get .1" on a harbour freight machine.

That means it's 6X faster to make the same part on the bridgeport. When you get in to mold making that's 6 hour programs regularly. It's just not economic to do on a small machine. Who wants to watch a machine for 36 hours when for another $1000 you could have bought the right tool in the first place.

“and when the average REAL CNC mill costs ~$10K(for a basic HAAS) then it’s stupid to condemn options in the <$2K range."

I don't know where you bought your Haas mill, mine was $100,000 with the indexer. I condemn the sub $2000 mills not on their price–but on the performance of them, lacking reliability and preciseness.
I also have mills that are comparatively cheap.
I bought a non-working $1600 cnc knee mill that had been hit by lightning–no control.
I put on a Fagor cnc control and new servos, and
limit switches, etc. and have a fully
functional *cast iron* commercial mill
with a 5hp spindle and 10" x 50" table
for less than $4000 total.
Compared to the benchtop homemade mills
talked about here, my retrofit was a lot more machine for not much more money.

Unfortunately, I will have to sell it
soon to make room for some new equipment
–know anybody interested?